When a cell divides – a process known as mitosis – its chromosomes must be separated and evenly distributed in the newly formed daughter cells. Although it is known to be extremely complicated and contains many cellular components, many of its details remain unclear, which has hindered efforts to develop treatments when mitosis goes wrong.
A new study reported in the journal Biology of natural cells he provided a deeper insight into this process, revealing the details of how protein complexes accumulate in the centers of chromosomes, in places known as centromeres. In these places protein complexes act as anchors, thanks to which cell structure organizers can redistribute chromosomes in the cell.
These protein complexes on centromere are known as kinetochores, to which long, thin, cylindrical structures called microtubules are attached. In the division, microtubule cells can physically manipulate chromosomes, pulling half of each chromosome to be included in one daughter cell and half to the other.
In this new study, a team led by Osaka University focused on various components that create and bind kinetochores. One such group is CCAN proteins that are present in the centromere throughout the cell cycle and act as a binding site for other microtubule binding proteins only when there is cell division. This work demonstrates that the subgroup of CCAN proteins that make up the CENP-T pathway predominates in ensuring successful cell division by binding to a protein complex called the Ndc80 complex, allowing microtubules to attach to chromosomes.
'We mainly studied whether the CENP-T pathway or the approximately similar CENP-C pathway is necessary for mitotic progression by selectively removing portions of these proteins that bind to the Ndc80 complex,' says author Tatsuo Fukagawa. "CENP-T mutants with no domains to bind to Ndc80, but not with similar CENP-C mutants, revealed the lack of chromosomes to segregate, preventing cell division and ultimately leading to cell death."
To confirm their results and to reveal more about the important role of CENP-T in promoting cell division mediated by the Ndc80 complex, the team also constructed chimeric constructs composed partly of CENP-T and partly of CENP-C. This confirmed the statement that CENP-T and molecules that bind to it are necessary for mitosis. They also explained that phosphorylation plays an important role in regulating the binding between the Ndc80 complex and CENP-T and has obtained additional direct evidence for their discovery by measuring the tractive force exerted by the microtubules in the mitotic spindle.
"Our work refutes the earlier consensus, showing that CENP-T, not CENP-C, works through the Ndc80 complex for successful cell division by ensuring accurate and timely segregation of chromosomes," says lead author Masatoshi Hara. "The findings can lead to therapeutic options in the treatment of diseases related to kinetic dysfunction and mitotic progression, including cancer."
The two-stage process ensures that key protein is maintained in the cell division
Masatoshi Hara et al, Multiple phosphorylations control recruitment of the KMN network to kinetochores, Biology of natural cells (2018). DOI: 10.1038 / s41556-018-0230-0